It is common in modern optical networks for the ingress of the transport network to use an optical transponder as a termination point for converting a ‘gray’ low cost optical signal from a customer's optical interface to a ‘colored’ optical signal on a service provider's network element. The ‘colored’ optical signal, or Wavelength Division Multiplex (WDM) signal, is typically enhanced, or ‘digitally wrapped’ with Optical Transport Network (OTN) overhead to provide service transparency, performance management capabilities and Forward Error Correction (FEC) coding for increased optical reach across the transport network. The WDM signal may then be transmitted across one or more optical links and through numerous intermediate devices before reaching the egress point of the transport network. At the egress point the WDM signal is terminated optically, the OTN overhead is removed and processed, and the remaining signal is converted back to a ‘gray’ low cost optical signal for transmission to the customer.
The transponder serves as the demarcation point between the operation, control and ownership of facilities of the service provider's network, hereafter referred to as SP, and the customer premise equipment. Examples of customer premise equipment may include a server, router or switch located at the campus of a business or it could be a WDM Terminal or Reconfiguration Optical Add Drop Multiplexer (ROADM) edge node from an SP in a different administrative domain.
FIG. 1 shows an example network wherein the operation, control and ownership domain of the SP is depicted in the shaded portion of the figure while the operation, control and ownership domain of the customer is depicted in the un-shaded portion of the figure. Since the network element of the SP performs optical-to-electrical-to-optical (OEO) conversion on each incoming and outgoing signal to and from its network, it is able to isolate and verify the quality of the received customer optical signal as it enters the SP's network and it is able to isolate and verify the quality of the WDM optical signal within its network. If there is a problem, the SP is able to identify the source of the problem as either within or outside of its own network.
Routing high speed optical signals across the transport network is very complicated. The signals may traverse long distances over multiple spans and through numerous nodes each of which may contain various components that impact the end to end quality of the optical signal. Example intermediate devices may include amplifiers (Erbium Doped Fiber Amplifier (EDFA) and Raman) and ROADMs of different types; all of which have the potential to impair the optical signal.
The SP's network management and control system uses its knowledge of the transport optical path to determine the availability and feasibility of any given channel taking into account factors such as dispersion and non-linear effects that may be a function of channel wavelength, modulation format, bit rate/line coding and/or minimum and maximum launch and receive channel powers, among others.
A transponder at each edge of the SP's network provides the necessary control logic for ensuring that the launch and receive powers and the signal quality are within acceptable tolerances given any impairment effects within the transport network. Although transponders can be expensive, take up a significant amount of space, consume a lot of power and require extensive cooling to function properly, they enable the SP to offer and verify service level guarantees to their customers.
For years the industry has explored the option of developing an all optical transport network that is protocol independent and bit-rate agnostic without the use of OEO conversions at the edge of the SP's network. To this end, customers have requested support for ‘alien’ wavelengths by the SP's and equipment suppliers. An alien wavelength is a WDM compliant wavelength that is originated by an optical interface that is not part of the SP's equipment. Support for alien wavelengths has the potential to reduce total equipment costs by moving the WDM optical interface to the customer node thus eliminating the ‘gray’ optics between the SP and the customer. It also has the potential to reduce capital and operational costs of the SP by reducing equipment, space, power and cooling requirements through the elimination of transponders. Further, it has the potential to simplify the structure of the network through the removal of the separate customer to SP spans and the corresponding separate fault and performance management segments at each end of the network. Finally, by enabling true end-to-end control and monitoring of a connection, both the SP and the customer may have a consistent view of the fault and performance management properties of the facility.
Given the complexity of ensuring end to end quality of the optical signal across the transport network, providing support for alien wavelengths has numerous control and management challenges that must first be resolved to ensure proper end to end operation. Considerations include operational procedures for channel setup, teardown, maintenance and management of channel optical parameters as well as fault sectionalization of the customer/service provider interface.
Current proposals for the support of alien wavelengths include the ITU-T Recommendation G.698.2 (November/2009) “Amplified multichannel dense wavelength division multiplexing applications with single channel interfaces” and the IETF draft draft-kunze-698-mgmt-ctrl-framework-00 (Jul. 1, 2011) “A framework for Management and Control of optical interfaces supporting G.698.2”, both included herein by reference. Both describe a ‘black link’ approach where the WDM transceiver is located at the customer node, or site, without the need for ‘gray’ optics. The ITU recommendation defines the channel optical parameters for a single optical interface as defined at the S interface (ingress to optical network) and R interface (egress from optical network). The IETF draft defines a high level framework for a necessary connection between the CPE's domain and that of the SP.
An example of a black link approach is depicted in FIG. 2. The tasks associated with configuration, provisioning and operation can be segmented and distributed across the domains of the customer and SP using a direct connection between the management systems of each. However, this approach adds a lot of complexity to operational procedures as well as to the design of the management and control systems. For instance, determination of center frequency and the channel setup procedure is controlled by the domain of the customer while other procedures are under the control of the SP. For an SP that typically performs interoperability testing of new equipment before actual deployment on its network, verifying the interoperability with a large number of customer domain management systems can require a significant effort.
A further method, such as those of U.S. Pat. No. 7,773,539 or its continuation-in-part U.S. Pat. No. 7,924,746, both disclosed herein by reference, defines a Virtual Transponder (VTXP) wherein a WDM interface in a router in one domain is modeled as a logical optical interface in the SP optical network element in a different domain and a control channel is established between the network management systems of each domain. The control channel exchanges information that can be used to negotiate, configure and/or manage the WDM interface on the router. The virtual transponder protocol converts messages between the domains in each management system. For example, a Link Management Protocol process runs between the NE controllers of each corresponding network element.
Although both approaches above enable the SP to get access to information related to the optical parameter settings of WDM optics, they still fall short of the traditional model where the SP has independent control over all WDM optical signals entering their network. To more accurately model the traditional approach used by the Service Provider, requires co-ordination and communication between the SP and customer domains. In particular, none of these approaches provide the SP with the ability to control access of an optical signal into their domain independent of control actions requested or required of the other domain.
FIG. 3 depicts an approach for a remote demarcation device that utilizes native WDM interfaces on the customer equipment at each end of the optical link such that these interfaces can share operational information with each other using unused overhead bytes of an OTN framing structure, such as that disclosed in US patent application US20090317073, included herein by reference. Unfortunately, this type of demarcation point also does not meet the objectives of the traditional demarcation point where the WDM interfaces are directly under the control of the SP. This approach allows information to flow between two WDM interfaces, each at a different location, but does not provide a mechanism that allows the SP to control access to the transport network before the connection is even established. This approach may augment support for alien wavelengths, but it has some of the same problems as the ‘black link’ approach in terms of control over access of the optical signals into the SP's network.
An apparatus, method and system for supporting alien wavelengths or which allows placing the WDM transceivers at the customer site without breaking the traditional model of independent control currently employed by the SP is preferred. At the very least, access to the transport network that is based upon direct knowledge of one or more of the optical properties of the WDM optical signal must be directly under the control of the SP's management system. Preferably, direct control of the channel optical parameters of the WDM optical signal and control over key operational procedures of the WDM optical channel should be handled by the SP. It is also desirable that such apparatus and method not preclude the option of using a segmented or integrated management solution as discussed above. Finally, it is desirable that the service provider has the option of sharing, in a read-only manner, information that it directly controls with the customer.